I have a 2007 Aero. I love the bike. It's a very good all-around bike, especially for the price.
That said, I think it depends on what you mean by "go on the highway." Certainly I "go on the highway" with mine. It can handle that just fine. However, if I was planning to do long distance tours, or if I intended to do daily commutes of 20 miles or so on an interstate, I'm not sure I would pick the Aero as my first choice. I would do it with my Aero, because it's the bike I own. But if I were choosing a bike for that, I think I'd go a little bigger.
The Aero is happiest at low rpm's. It chugs along and sounds great, feels great. There's no tach, so I'm guessing, but I'd say 2,000 to 2,500 rpm's is a good comfort zone for regular driving.
At 70, on the Aero, you are well above that rpm level. The bike is winding pretty tight. I sometimes wish there was a sixth gear to drop into. I mean, it's fine, and it is well within the overall rpm range that the bike is intended for. I just sometimes wish it could cruise at 70 without the engine running that fast.
Again, it's a great bike, and if you simply are asking is it "highway capable," absolutely.